Open cluster members in APOGEE DR17

I. Dynamics and star members

¹ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
² Observatório Nacional / MCTI, R. Gen. José Cristino, 77, 20921-400 Rio de Janeiro, Brazil
³ Departamento de Física, Universidade Federal de Sergipe, Av. Marcelo Deda Chagas, S/N Cep 49.107-230, São Cristóvão, SE, Brazil
⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA
⁵ NSF’s NOIRLab, 950 N. Cherry Ave. Tucson, AZ 85719, USA
⁶ Departamento de Matemática, Facultad de Ingeniería, Universidad de Atacama, Copiapó, Chile

^★ Corresponding authors: rafael.fraga@ucn.cl; jose.fernandez@ucn.cl

Received: 4 April 2025
Accepted: 16 June 2025

Abstract

Context. Open clusters (OCs) are groups of stars formed from the same cloud of gas and cosmic dust. They play an important role in studies of star formation and evolution and our understanding of galaxy structure and dynamics.

Aims. The main objective of this work is to identify stars that belong to OCs using astrometric data from Gaia EDR3 and spectroscopic data from APOGEE DR17. Furthermore, we investigate the metallicity gradients and orbital properties of the OCs in our sample.

Methods. By applying the HDBSCAN clustering algorithm to these data, we identified observed stars in our galaxy with similar dynamics, chemical compositions, and ages. The orbits of the OCs were also calculated using the GravPot16 code.

Results. We find 1987 stars that tentatively belong to 49 OCs; 941 of these stars have probabilities above 80% of belonging to OCs. Our metallicity gradient presents a two-slope shape for two measures of different Galactic center distances – the projected Galactocentric distance and the guiding center radius to the Galactic center – as already reported in previous work. However, when we separate the OCs by age, we observe no significant difference in the metallicity gradient slope beyond a certain distance from the Galactic center. Our results show a shallower gradient for clusters younger than 2 Gyr than those older than 2 Gyr. All our OCs dynamically assemble the disk-like population very well, and they are in prograde orbits, which is typical for disk-like populations. Some OCs resonate with the Galactic bar at the Lagrange points L4 and L5.